In the prior funding period we have introduced a new approach to genetic mapping in inbred rodent strains that exploits closely related lines differing in traits of interest. Using a 10K SNP map, we have shown that two SHR lines differ at only 13% of their genomes, but that these differences have a profound effect on susceptibility to hypertensive renal disease. The close genetic similarity has allowed us to perform fine mapping that has resulted in the identification of three highly resolved quantitative trait loci (QTL) affecting blood pressure and renal injury. Because of the similarity between the lines, each of these QTL maps to a small, isolated block where the two SHR lines have descended from different ancestors. These blocks are surrounded by extensive regions that are identical-by-descent (IBD) and thus help to narrowly define the QTL's, down to a small number of genes. In the present study we propose to identify the genes in each QTL that contribute to increased hypertensive renal disease and to understand the mechanisms by which they act. One QTL has effects on both blood pressure and renal injury. We seek to identify the causative variation and determine whether it acts first on blood pressure with secondary effects on injury or whether it lies in a pathway that produces injury that then leads to reduced renal function and increased blood pressure. Another QTL has no effect on blood pressure and appears to lead to glomerular damage directly. We have also identified the immunoglobulin heavy chain as a locus containing extensive variation across our lines. We have shown that this includes variation with important effects on IgG function including the inability to transfer IgG from mother to offspring. This variation associates with increased albuminuria. We propose to investigate whether alterations in immune function that are encoded by differences in the heavy chain of immunoglobulin contribute to the emergence of renal disease in the susceptible SHR line and whether maternal-offspring IgG transfer is involved in the transmission of risk. We have identified allelic variatio in IgG in humans that is widespread and ancient and that is functionally homologous to the variation we detected across SHR lines. We will perform a large-scale human population genetic study to determine the association of this variation with renal function in humans.